Update Lib_usage.ml

[Halbaroth]

We have changed a bit the API of the AE library but the Lib_usage.ml isn't up to date.

I don't know why I prevented Dune from compiling this file, so I restore the compilation and the test of this file.

[Halbaroth]

Actually, @bclement-ocp suggested to remove the compilation of examples: #796 (comment)

Do you have any reason? I can move the Lib_usage.ml file.

[bclement-ocp]

I admit I don't remember the details but I believe it was actually a dune configuration problem and the examples were introducing bogus dependencies on the OPAM CI; it's not a problem to build the examples in general.

I am not sure why I suggested to not build the examples; I think the issue is lack of a (package) stanza (probably (package alt-ergo-lib)).

[Halbaroth]

(executable
 (name Lib_usage)
 (public_name lib-usage)
 (package alt-ergo-lib)
 (libraries AltErgoLib)
 (modules Lib_usage)
)

?

[bclement-ocp]

I am not sure; I think we need to make sure that all of the following are OK (again my memory is fuzzy but if I recall correctly the examples were run for the parsers):

$ dune clean && dune build -p alt-ergo-lib @runtest
$ dune clean && dune build -p alt-ergo-parsers @runtest
$ dune clean && dune build -p alt-ergo @runtest

If all of these pass and the Lib_usage is run only in one of them (probably not parsers) then we should be fine.

[bclement-ocp]

LGTM provided that the aforementioned CLI commands succeed 👍